Pd (II)‐catalyzed vinyl addition polymerization of novel functionalized norbornene bearing dimethyl carboxylate groups

Three novel functionalized polynorbornenes (PNB) with pendant dimethyl carboxylate group (carboxylates—acetate, propionate, and butyrate) are synthesized as a vinyl‐type with a palladium (II) catalyst in high yield. The effects of size of substitutents, molar ratio of monomer to catalyst, solvent polarity, reaction time, and temperature on the polymerization of exo‐norbornene dimethyl propionate were systematically investigated. The low molar ratio and temperature, as well as high polarity of solvent, and long reaction time, are favorable for the enhancement of the monomer conversion, especially, the solvent have an obvious effect on the catalyst activity. The resulting poly(cis‐norbornene‐exo‐2,3‐dimethyl carboxylates) (PNB‐dimethyl carboxylates) show good solubility in common organic solvent and high thermal stability up to 360 °C. The glass transition temperature was detected by DMA at 331, 324, and 318 °C for acetate, propionate, and butyrate, respectively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3391–3399, 2007     

MODELING HARVEST SCHEDULING IN MULTIFUNCTIONAL PLANNING OF FORESTS FOR LONGTERM WATER YIELD OPTIMIZATION

In this study, wood production and hydrologic functions of forests were accommodated within a planning procedure for separate working circles (areas dedicated to certain forest functions) that were delineated according to an Ecosystem‐Based Functional Planning approach. Mixed integer goal programming was used as the optimization technique. The timing and scheduling of a maintenance cutting (partial harvest) was the decision variable in the modeling effort, and an original formulation was developed as a multiobjective planning procedure. Four sample planning strategies were developed and model outputs were evaluated according to these strategies. Spatial characteristics of stands were considered, and used to prohibit the regeneration of adjacent stands during the same time period. Because of the positive relationship between qualified water production and standing timber volume in the forest, the model attempts to maximize qualified water production levels by increasing standing volume stocks in the forest through the delay of regeneration activities.     

Effect of chemical modification on oligomerization capacity of alumina support for Pd-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Effect of modification with an alkali metal on the acid properties of alumina supports and on the oligomerization capacity and working stability of Pd-Al₂O₃ catalysts was studied.     

Photoionization of small krypton clusters in the Kr 3d regime: evidence for site-specific photoemission

Kr 3d ionization energies of small, variable size krypton clusters are investigated by photoelectron spectroscopy, where the size regime of clusters with an average size N< or =30 is studied. Characteristic shifts in Kr 3d ionization energies to lower binding energies are found compared to the bare atom. These are also different from those of large krypton clusters. Moreover, we find evidence for photoionization of the krypton dimer. Its 3d ionization energy is barely shifted relative to the atomic value. Results from model calculations considering different isomers and cluster sizes as well as defect sites give evidence that the experimental results can be related to photoionization from different surface sites in variable size krypton clusters. This can be related to site-specific photoemission in small Kr clusters. The results are compared to size effects in Kr 3d near-edge features of variable size Kr clusters as well as recent results on Kr 3d photoionization of large Kr clusters.     

An electronic signature of hydrolysation in the X-ray absorption spectrum of aqueous formaldehyde

Formaldehyde in aqueous solution is hydrolysed and forms methanediol. Using X-ray absorption spectroscopy we show that the hydrolysation product can be identified by a distinct electronic signature in the spectra. This is manifested by the disappearance of the oxygen 1s → π* absorption line. The X-ray absorption spectrum of aqueous formaldehyde is compared with those of the structurally similar formamide and urea, which are in contrast not hydrolysed in aqueous solution. We thereby demonstrate the exceptional sensitivity and simplicity of the technique to monitor this fundamental process in the aqueous phase.     

Synthesis and cytotoxicity of 28-carboxymethoxy lupane triterpenoids.Preference of 28-O-acylation over 28-O-alkylation of betulm by ethyl bromoacetate

28-Carboxymethoxy lupane tritepenoids 3 and 4 were synthesized by alkylation of betulin with the THP protected 2- hydroxyethyl iodide followed by oxidation and reduction.Direct reaction of betulin(5) or betulone(10) with ethyl bromoacetate led to 28-O-acylation,instead of 28-O-alkylation.The targeted compounds 3 and 4 were not cytotoxic at the highest concentration tested(75μmol/L),suggesting that elongation of the chain length at the 28-position in both betulinic acid(1) and betulonic acid(2) was detrim...     

Plasmon single- and multi-quantum excitation in free metal clusters as seen by photoelectron spectroscopy

Plasmons are investigated in free nanoscale Na, Mg, and K metal clusters using synchrotron radiation-based x-ray photoelectron spectroscopy. The core levels for which the response from bulk and surface atoms can be resolved are probed over an extended binding energy range to include the plasmon loss features. In all species the features due to fundamental plasmons are identified, and in Na and K also those due to either the first order plasmon overtones or sequential plasmon excitation are observed. These features are discussed in view of earlier results for planar macroscopic samples and free clusters of the same materials.     

Site-dependent spectral shifts in core-to-pi* excitations of pyridine clusters

Site- and element-selective core-to-pi* excitation in free pyridine clusters is investigated. The experimental results indicate the occurrence of site- and size-dependent spectral shifts in the C 1s and N 1s --> pi* excitation regime. Specifically, we observe in the C 1s regime a substantial and site-dependent redshift of the low energy slopes of the C 1s --> pi* band by 90 meV in clusters relative to the bare molecule, whereas the high energy slopes of this band remain almost unchanged. In contrast, a size-dependent blueshift of the same order of magnitude is found for the entire N 1s --> pi* band. This is distinctly different from previous results on van der Waals clusters, where exclusively redshifts in 1s --> pi* transitions are observed. The experimental results are compared to ab initio calculations, which serve to simulate the 1s --> pi*( v = 0) transitions. These results clearly indicate that the spectral shifts are primarily a result of electrostatic interactions between the molecular moieties and that an antiparallel orientation of molecular units preferably dominates in variable-size pyridine clusters.     

Theoretical study on the electronic,structural, properties and reactivity of a series of mono-, di-, tri- and tetrachlorothiophenes as well as corresponding radical cation forms as monomers for conducting polymers

In this paper, electrical and structural properties of mono-, di-, tri- and tetrachlorothiophenes and their radical cations have been studied using the density functional theory and B3LYP method with 6-311++G** basis set. The effects of the number and position of the substituent of chlorine atoms on the properties of the thiophene ring for all chlorothiophenes and their radical cations have been studied. Vibrational frequencies, nuclear chemical shielding constants, spin-density distribution, size and direction of dipole moment vector, ionization potential, electric polarizabilities and NICS values of these compounds have been calculated as well. The analysis of these data showed that double bonds in 3-chlorothiophene are more delocalized and it is the best possible candidate monomer among all chlorothiophenes for the synthesis of corresponding conducting polymers with modified characteristics.     

Cluster size effects in core excitons of 1s-excited nitrogen

Cluster size effects in core excitons below the N 1s ionization energy of nitrogen clusters are reported in the energy regime 405-410 eV. These results are compared to the molecular Rydberg states as well as the corresponding bulk excitons of condensed nitrogen. The experimental results are assigned using ab initio calculations. It is found that the lowest excitons (N 1s-->3ssigma and N 1s-->3ppi) are blueshifted relative to the molecular Rydberg transitions, whereas others (N 1s-->3dpi and N 1s-->4ppi) show a redshift. Results from ab initio calculations on (N(2))(13) clearly indicate that the molecular orientation within a cluster is critical to the spectral shift, where bulk sites as well as inner- and outer-surface sites are characterized by different inner-shell absorption energies. These results are compared to the experimental spectra as well as previous work on site-selectively excited atomic van der Waals clusters, providing an improved spectral assignment of core exciton states in weakly bound molecular clusters and the corresponding condensed phase.